The licensee provided the following report via facsimile:
On February 3, 2005 at 1819 hours0.0211 days <br />0.505 hours <br />0.00301 weeks <br />6.921295e-4 months <br />, Quad Cities Nuclear Power Station (QCNPS) confirmed a vulnerability with a 4160 VAC relaying and metering current transformer (CT) associated with the Unit and Reserve Auxiliary Transformers (i.e., the UAT and RAT) on both Unit 1 and Unit 2. Although the CT is currently fully operable, failure of the CT circuitry could cause the neutral overcurrent relay to trip and lockout the circuit breakers supplying feeds to safety related buses 13 (23) and 14 (24), isolating them from their normal and emergency power sources. Emergency power (i.e., the emergency diesel generator) would still be available to supply power to safety related buses 13-1 (23-1) and 14-1 (24-1), but the Residual Heat Removal Service Water (RHRSW) system may be without a source of power. If this failure occurred during a LOCA, then the RHRSW pumps may not be started within the ten minute requirement. A modification is in progress to eliminate this vulnerability. This event is being reported as a potential loss of safety function (10CFR50.72(b)(3)(v)(B)) and as a degraded or unanalyzed condition (10CFR50.72(b)(3)(ii)(B)).
The NRC Resident Inspector has been notified.
See similar events #41362 (Crystal River), #41366 (LaSalle), and #41370 (Dresden).
